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Can severe drought reverse woody plant encroachment in a temperate A ustralian woodland?
Author(s) -
Zeeman Ben J.,
Lunt Ian D.,
Morgan John W.
Publication year - 2014
Publication title -
journal of vegetation science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.1
H-Index - 115
eISSN - 1654-1103
pISSN - 1100-9233
DOI - 10.1111/jvs.12153
Subject(s) - basal area , woodland , woody plant , temperate climate , biology , ecology , grassland , temperate rainforest , forestry , agroforestry , geography , ecosystem
Question Increases in the cover of woody plants have been documented in woodland, savanna and grassland ecosystems across the globe, commonly attributed to changes in land use or disturbance regimes. This is often thought to result in alternative stable states resistant to reversal. However, some multi‐decadal‐scale studies have found woody plant cover fluctuates according to variations in rainfall. After a decade‐long E l N ino event, we ask: can severe drought reverse woody plant encroachment in a temperate A ustralian woodland? Location Temperate coastal woodland in V ictoria, SE A ustralia that has remained unburned for over a century. Methods Using data spanning 41 yr, changes in basal area and tree density were assessed for the major woody species in a eucalypt woodland. Data were used to determine whether a decade of severe drought (1997–2009) had reversed a previously identified phase of woody plant encroachment (1971–1996). Results After an increase in stand density between 1971 and 1996, attributed to an increase in the fire‐sensitive species A llocasuarina littoralis , total tree density then declined by 42% between 1996 and 2012. Changes in tree density differed across dominant woody species ( A . littoralis −34%, A llocasuarina verticillata +26%, A cacia pycnantha −78%, B anksia marginata −73%, E ucalyptus spp. −97%), and seedling recruitment almost completely ceased for all species. However, the basal area of A . littoralis (having almost doubled between 1971 and 1996) had continued to increase by 75%, with increases highest in areas where initial basal area was lowest. Despite this increase, total stand basal area remained relatively stable, with an increase of 5%, because of a combined decline in basal area for all other species of 62%. Conclusion Despite the most severe drought on record, site occupancy – as measured by basal area – did not decline between 1996 and 2012. Thus, severe drought did not reverse woody plant encroachment. Rather, findings were consistent with the previous trend of increasing A . littoralis dominance at the expense of other tree species in the long‐term absence of fire.